In semiconductor fabrication, a photoresist material is used for transferring a photomask pattern onto one or more material layers, for example, transferring a photomask pattern onto a metal layer, a dielectric layer or a semiconductor substrate. However, with continuous shrinking of the feature size in semiconductor processes, it becomes increasingly difficult to form a photomask pattern having a smaller feature size and to transfer the photomask pattern onto a material layer using a photolithography process.
In order to reduce the influence of optical proximity effect, photolithography resolution enhancement techniques have been proposed in industry. Among the photolithography resolution enhancement techniques, double patterning technology (DPT) is regarded as a powerful technique to fill a gap between immersion lithography and extreme ultraviolet lithography (EUV). In DPT, an etch sacrificial layer is usually formed on a to-be-etched material layer. Sidewall spacers are formed around the etch sacrificial layer. After the etch sacrificial layer is removed, the to-be-etched material layer is etched using the sidewall spacers as an etch mask. A pattern having a small feature size can thus be formed.
FIGS. 1-4 depict cross-sectional views of a conventional double pattern at various stages during its formation. Referring to FIG. 1, a to-be-etched material layer 101 is provided. A hard mask layer 102 is formed on the to-be-etched material layer 101. A plurality of discrete sacrificial layers 103 are formed on the hard mask layer 102.
Next, referring to FIG. 2, a sidewall-spacer material layer 104 is formed to cover the sacrificial layers 103 and the hard mask layer 102. Then, referring to FIG. 3, the sidewall-spacer material layer 104 is etched using a maskless etching process, to form sidewall spacers 105 on sidewalls at both sides of each sacrificial layer 103. Referring to FIG. 4, the sacrificial layers 103 (referring to FIG. 3) are then removed. The sidewall spacers 105 that remain can be used as a double-patterning mask.
However, the double pattern formed using the existing double-patterning technology tends to be deformed easily, as shown in FIG. 4. Thus, subsequent etching of the hard mask layer and the to-be-etched material layer can be affected. The disclosed methods and structures are directed to solve one or more problems set forth above and other problems.